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12                                    CIVET   AND   MUSK

their darker' coat In the spring. This is, however, only an
extreme case of a change which is general. Most animals get
a thicker fur In winter and exchange It for a lighter one in
summer. And the hues of the coat change in correspondence.
Glands of the Skin.  The great variety of integumeiital
glands possessed by the Mammalia distinguishes them from any
group of lower Vertebrates. This variability, however, only con-
cerns the anatomical structure of the glands In question. Histo-
loglcally they are all of them apparently to be referred to one of
two types, the sudoriparous or sweat gland and the sebaceous
gland. Simple sweat and sebaceous glands are abundant In
mammals, with but a few exceptions. The structures that we are
now concerned with are agglomerations of these glands. The
mammary glands will be treated of in connexion with the mar-
supium; they are either masses of sweat glands, or of sebaceous
glands whose secretion has been converted into milk.
Many Carnlvora possess glands opening to the exterior, near
the anus, by a large orifice. These secrete various odoriferous
substances, of which the well-known " civetM is an example.
Other odoriferous glands are the musk glands of the Musk-deer
and of the Beaver ; the suborbital gland of many Antelopes ; the
dorsal gland of the Peccary, which has given the name of
Dicotyles to the genus on account of its resemblance In form to
a navel. This gland may be seen to secrete a clear watery fluid.
The Elephant has a gland situated on the temple, which is said
to secrete during certain periods only, and to be a warning to
leave the animal alone. Very remarkable are the foot glands of
certain species of Ktiinoceros ; they are not universally present
in those animals, and are therefore useful as specific distinctions.
On the back of the root of the tail In many Dogs are similar
glands. The Gentle Hemur (Hapalemur) has a peculiar gland
upon the arm, about the size of an almond, which in the male
underlies a patch of spiny outgrowths. In Lemur varius is a
hard patch of black skin which may be the remnants of such
a gland. It is thought that the callosities on the legs of Horses
and Asses are remnants of glands.
One of the most complex of these structures which has been
examined microscopically exists in the Marsupial Hfyrmecolri'us.1
On the skin of the anterior part of the chest, just In front of the
1 Proc. Zool. Soc. 1887, p. 527.